Process control systems utilize a variety of field devices to control process parameters. Fluid valves and regulators are commonly distributed throughout process control systems to control the flow rates and/or pressures of various fluids (e.g., liquids, gasses, etc.). In particular, fluid regulators are typically used to regulate the pressure of a fluid to a substantially constant value. Specifically, a fluid regulator has an inlet that typically receives a supply fluid at a relatively high pressure and provides a relatively lower and substantially constant pressure at an outlet. For example, a gas regulator associated with a piece of equipment (e.g., a boiler) may receive a gas having a relatively high and somewhat variable pressure from a gas distribution source and may regulate the gas to have a lower, substantially constant pressure suitable for safe, efficient use by the equipment.
Fluid regulators typically control the flow and pressure of fluid using a diaphragm having a set or control pressure force applied to one of its sides via a bias spring. The diaphragm is also coupled directly or via a linkage (e.g., a lever) to a valve plug that is moved relative to an orifice of a seat ring that fluidly couples the inlet of the regulator to its outlet. The diaphragm moves the plug in response to a difference between the outlet pressure and the set or control pressure to vary the flow restriction provided by the plug to achieve a substantially constant outlet pressure, which provides a balancing force to the other side of the diaphragm that is equal or proportional to the set or control pressure.
In addition to a seat ring, many fluid regulators have trim including a cage that interposes in the flow path between the inlet and outlet of the fluid regulator to provide certain fluid flow characteristics. For example, some cages may be designed to provide torturous or other types of flow paths to reduce noise associated with flowing fluid. Such noise reduction cages, commonly referred to as sound trim, may be particularly useful in applications where the regulator is in close proximity to people (e.g., household occupants or other building occupants). Other regulator trim designs provide cages that provide certain fluid flow or regulation characteristics to suit the needs of a particular control application. For example, the cages may be configured to provide particular, desirable fluid flow versus pressure drop characteristics. Still further, regulator trim designs may also provide different types of seats or seat rings. For example, the size of the orifice may be varied to provide a more restricted seat (i.e., a seat that provides a relatively higher pressure drop at any given fluid flow rate) or a less restricted seat (i.e., a seat that provides a relatively lower pressure drop at any given flow rate).
However, known regulator trim utilizing a cage typically provides the cage and seat ring as a unitary or one-piece structure. Such a unitary or one-piece trim configuration eliminates the possibility of tolerance stack up that could occur if multiple components were used. In particular, the alignment of the cage and/or seat with the regulator body could be compromised by the cumulative tolerances of multiple, separate trim components. Further, such known unitary or one-piece trim enables the regulator to be used in certain vertical applications (e.g., where the bonnet is vertically oriented and pointing downward. In such vertical applications, if the regulator trim is to be serviced (e.g., replaced), installation of replacement trim would be very difficult, if not impossible, if the trim were not of a unitary or one-piece construction. In particular, the installation (e.g., stacking) of multiple trim components would likely result in a first installed component falling out of a desired mounting position and/or the regulator body (i.e., falling downward) while a second component is installed on top of the first component.
Yet another known regulator trim configuration provides only a seat ring (i.e., a seat ring without an integral cage), which is held in place within the regulator by pins. One such known configuration may be found in the EZH and EZL regulator products manufactured by Fisher Controls International LLC.